1. Field of the Invention
The present invention relates to a recording medium transport device that nips and transports a recording medium, and an image forming apparatus including the recording medium transport device and a printing part.
2. Background Art
Conventionally, in an apparatus for forming an image by causing ink jetted from a nozzle of an ink-jet recording head to adhere to a recording medium, the recording medium is made to intermittently move (step feeding) a specified length in a sub-scanning direction, and during the stop of the intermittent movement, a carriage on which the recording head is mounted is moved in a main scanning direction, and an image is formed in every specified area.
In that case, in JP-A-2002-154701, an upstream side transport roller pair at a transport upstream side (hereinafter simply referred to as an upstream side) in a sheet transport direction and a downstream side transport roller pair at a transport downstream side (hereinafter simply referred to as a downstream side) are disposed at both sides of the recording head, the recording medium is nipped by both the roller pairs, and both the roller pairs are intermittently driven through a multistage gear train from one drive motor (transport motor) so that the recording medium is moved in the sub-scanning direction.
According to the structure of JP-A-2002-154701, since the gear train is constructed in multi-stages, there has been a problem that a large space is required to dispose the large and small gears. Besides, as one of methods for actuating (operating) gears quietly, there is known a method of increasing contact ratio, however, a normal spur gear cannot raise the contact ratio. As another method of increasing the contact ratio, there is a method of using helical gears, however, there arises a problem that a drive load occurs in a thrust direction.
In order to actuate (operate) a gear quietly, for example, Japanese Patent No. 2710861 discloses such a gear that plural (for example, two trains) gear trains (spur gear trains) having the same circumferential pitch are formed on the peripheral surface of a single gear substrate by integral molding, each of the gear trains is shifted from the adjacent gear train by a half pitch (½ pitch), and part of a dedendum of each gear tooth of each gear train is integrated with part of dedendum portions of front and back gear teeth of the adjacent gear train through uniform crossing surfaces.